


Heat Machine

by Bluelinklover



Category: Undertale (Video Game)
Genre: Fellcest - Freeform, Fontcest, M/M, Skeleheat, implied rape, well Underfell sans wants boss to rape him lel
Language: English
Status: Completed
Published: 2016-07-07
Updated: 2017-10-09
Packaged: 2018-07-22 05:12:12
Rating: Mature
Warnings: Graphic Depictions Of Violence, Rape/Non-Con
Chapters: 3
Words: 2,170
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/7421284
Author URL: https://archiveofourown.org/users/Bluelinklover/pseuds/Bluelinklover
Summary: <blockquote class="userstuff">
              <p>Everything is going well in the timeline that merged Undertale, Underfell and Underswap. Until someone creates a machine that sends sub monsters into heat.</p><p>(Made for @trashfontcesttrash on tumblr. Don't like don't read, first Undertale fanfic.)</p>
            </blockquote>





	1. Chapter 1

Fell was having a horrible day. First some wacko created a machine that forces monsters into heat, then he had to listen to the Underswap royal scientist nag at him about being careful until the rogue scientist was captured.

He just wanted to go home and relax. On his way home Fell stopped at the store to pick up something easy to make for dinner tonight, it was his night to cook and he didn't want to.

When he opened the front door the first thing he noticed was a sweet smell. Sickeningly sweet. He headed to the kitchen and put the food away, he still had a few hours before the others come home from work. 

So he decided to watch tv. when he sat on the couch he was immediately bombarded by his brother. Oh he was so not in the mood. "Not now sans." Was all he said, he got a whine in response. 

"Sans I sai-" Fell was cut off when he saw his brother panting and sweating more then usual. "Sans? What's wrong?" he asked in a worried tone. He tried to move but it was like having greater dog sitting in your lap.

He wiggled but to no avail. he looked up and saw comic and blue staring at him, there cheeks flushed. 'Wait a fucking minute' he thought to himself.

"OH MY FUCKING GOD!" He yelled causing the sans' to jump. "I need to call Undyn!" He said to himself as he forced the sans' off of him. Who gave disapproving whines.

~~~~~~~~~~

"Yes that's right. Ok. Uhuh. Ok. Thanks." The phone clicked as Fell closed it with a sigh and went back inside. He informed swap alphys that he wouldn't be coming to work for a week or so. He explained why and she understood. 

"God dammit." Fell says to himself as he dialed the numbers to his other counterparts informing them that there brothers were in heat. They rushed home and had to pry the sans' away from each other. 

~~~~~~~~~~~

UT bros

"Shh, it's ok sans, it's gonna be ok." Chrisp says as he carries comic to their room. 'He's shaking like crazy and whimpering, it must be bad....' Chrisp thinks to himself as he walked in and shut the door. Locking it for good measure. 

He set comic on the bed, but as he lets go comic clings to him, It's.. Nice. He doesn't cling to chrisp. Not since the first time.... Chrisp hears him whimper and it pulls him from his thoughts. 

"P-papy......" Comic whimpers/moans as he writhes on the bed. "Shhh. It's alright." Chrisp says trying to be as soothing and calm as possible. But it's hard to stay calm when he see his brother in this much agony.

"P-pahhpy.. I-I need..." Comic starts to say then starts panting as he forms an ecto-pussy. Chrisp reaches down and starts pulling his clothing off. The more clothing he removes the the heavier he pants. 

Almost like a dog. It's kinda cute. As Chrisp removes the last of his clothing he can't help but notice how wet comic is. He take his gloves off and starts rubbing comics dripping cunt. 

"Mmmmmm~" comic moans as Chrisp slip a finger in his tight wet heat. It makes him moan louder. 'I love the way he sounds. I haven't seen sans in a heat this bad since I was 15. That's the first time he accepted my help.' Chrisp thinks to himself.

"P-Papyrus....." Comic says quietly. "M-More...." 

"You want more sans?" Chrisp asks softly. Comic moans in response.

"Alright, alright.. Just, Erm. Lay back and relax, ok?" He say as he helps get comic comfortable. After comic gets comfy Chrisp starts to caress his dripping ecto-pussy. Comic lets a low moan go as Chrisp plays with his clit. 

 

Comic grips his skull as Chrisp lean down, he forms a tongue and place it to tip to comics clit. Comic moans loudly, so Chrisp flicked his tongue as comic tightened his grip on his skull, this is a good sign. It means he likes it. 

Chrisp licked at comics clit for a good five minutes before He plunges his tongue into that wet pussy of his. Comic arched his back and thrust his pelvis up, causing Chrisps tongue to go deeper. He fucks comic with his tongue making him beg for more. 

Chrisp pulls away and comic gives a low whine of disapproval, Chrisp hushes him as he lines himself up. Comic makes a grabby motion at him and Chrisp leans closer, comic clings to Chrisp as if his life depended on it. 

Chrisp smiles softly as he slowly pushes in. Comic moans rather loudly as he does so. Soon he is buried to the hilt of that sweet pussy of comics. "mmmNNNNN!" Comic moans when he feels his brother brush up against his sweet spot.

"S-Sorry brother...." Chrisp says quietly as he nuzzles into the crook of comics neck bones. "'S ok..." Comic says as he hugs his brother tightly. "Y-You can move now pap." Comic says. "A-Alright brother." Chrisp says sweetly as he pulls out almost all the way, only to thrust back in.

Comic moans louder each time Chrisp thrusts. The sound drives him crazy. Chrisps thrust start to loose rhythm as he starts to loose control. Lost in his brothers heat. Eventually the thrusts become too much for comics smol figure. And he starts screaming in pain.

Chrisp stops suddenly when he realizes how rough he was being with his brother. "O-Oh God! I-I'm so sorry sans!" Chrisp says in a panic as comic pants heavily as he shakes. "I'm so sorry..." Chrisp whispers to him as comic clings to his brother like a lifeline. 

"Shhh. It's ok brother.. It's ok..." Chrisp says to his brother softly as he pulls out and thrusts back in. Only slower and much gentler this time. Comic moans again. Chrisp did a quick look over of his brother and deemed him uninjured. 'Stars....' Chrisp thinks to himself. 'Sans heat is so strong it's effecting me...'

Chrisp was so deep in thought he didn't even noticed comic wiggling underneath him until it was too late. Comic grabbed him brother and flipped so he was on top and Chrisp was on bottom. Chrisp looked up at his older brother just in time to see a crazed look in his eyes. 

"Paps..." Comic said quietly. "It hurts... I can't stand this heat any longer bro..." He said a bit louder this time. "Brother... It's alright, I'll help. You know I'll always help you." Chrisp said with a smile. Comic looked like he was going to cry before he pressed himself into crisps chest, sobbing quietly. 

Chrisp rolled them over and allowed his big brother to cry himself to sleep. When comic wakes up Chrisp will have to help him finish this little problem.


	2. Chapter 2

**Notes for the Chapter:**

> Sorry it took so long >~>

~~~Swap Bros~~~

Stretch sighs as he watches his brother writhing on the bed. "Bro... How do we end up in these messes..?" Stretch asks knowing he won't get an answer. "Mnnnn! Papy!" Blue whines loudly. "Yea yea I'm here bro, I'm here." Stretch says as he takes his hoodie off and throws it aside. 

After discarding his hoodie, stretch climbs on the bed and hovers over blue. Blue whimpers as stretch lays his skull in the crook of his neck, letting out a long sigh. "Please papy pleeeease~" blue whines in a needy tone. "I know bro I know." Stretch says soothingly. 

Stretch quickly strips blue of his sweaty clothes and runs a cold bath. Blue made whines and huffs of disappointment as he was placed in the soothing cold water. Stretch grabbed a washcloth and took his own clothes off before getting in the tub and sitting his little bro in his lap. 

Blue snuggled back into his brother as the cool wash cloth rubbed over his bare bones. He would moan and whimper every so often as the cloth hit a particularly sensitive spot. After about an hour of soaking in cold water, stretch leaned down and nipped blues shoulder blade, earning a very loud moan from his younger brother. 

Stretch discarded the cloth and put one of his hands between blues legs, fondling his pelvis. Blues moans get louder and needier as stretch let's his free hand roam and rub across the porcelain bones of his younger sibling. Blue bucks into stretches touch as he whines, begging his brother to fuck him senseless. 

"Easy bro, easy.." stretch whispers as he clanks blues skull in a kiss. "Please papy please..." blue whispers needily as his big brother starts to finger his dripping pussy. "Your already so wet bro~" stretch teases, earning an annoyed groan from blue. Stretch pulls blue closer as he removes his fingers, earning a whine from his brother. 

"Chill bro." Stretch says softly as he kisses blue before slipping his orange cock into blues tight little pussy. Blue makes a high pitched moan as he's roughly fucked by his brother, who moans and whispers compliments and praises in his ear as he pounds blues dripping wet cunt. 

Blue tenses and screams in pleasure as he cums. If it weren't for stretch holding him close he'd of went face first into the bath water. Stretch bucks into blue as he feels him tightening around him. Blue reaches an arm up and rests his hand on stretches skull moaning his big brothers name, again and again until he feels his brothers hips stutter as he cums deep inside him. 

As their breathing calms stretch slowly pulls out of his precious little blueberry before changing the bath water and washing them both off. After they finish their bath, stretch wraps blue in a fluffy towel and carries him back to bed. Blue whimpers a little as he sees his big brother crawl into bed with him. 

"Good night papy.." blue says with a soft yawn. "G'night bro." Stretch says back, kissing blue on the skull before tucking him is and falling asleep.

**Notes for the Chapter:**

> How ya likes it! Be sure to check out my Tumblr if ya have any questions. =w=


	3. Chapter 3

**Summary for the Chapter:**

> Sorry if its not good or what you expected, I've lost interest in undertale. But it was fun, i won't stop writing, i just won't be writing undertale any more ^^;

\---Fell Bros---

Fell struggled to get red to stay still. No matter what he did, he clung to him like a life line. "Sans calm down!" Fell yelled. Red flinched and whimpered, but calmed. Fell had never seen his brother in heat. He was surprised to find that he was so shy and timid, yet clingy. 

Fell sighed and leaned down, putting his face next to his brothers. "Sans.." he started. Red look up at him with lustful eyes. "I will help you but you need to at least try and control yourself." Fell says, placing a soft kiss to reds skull. Red nodded and tried his best to keep himself under control. 

Fell quickly stripped his clothes, then stripped reds. Grabbing the lube from the bedside drawer, he worked quickly to lube him and his brother up, making sure it was enough so he wouldn't hurt him. He rubbed reds wet cunt, pinching his clit and teasing him by poking and prodding. 

"Boooooooosssssss~!" Red whined. "No teasiiiiiing.." he wiggles and writhes underneath his papyrus, giving low impatient whines and huffs. Fell smirks, his bright red eye lights roaming up and down his jelly like body. "But I thought you liked teasing sans~?" He leaned down and blew a hot breath onto the side of reds neck causing him to shiver and mewl.

"N-Not when I'm in heat.." red replies in an almost whisper, continuing to wiggle and grind against his brother. "Please papy please.." he whimpers, nearly in tears. "Alright alright, easy now sans." Fell said softly as he grabs his length and rubs the tip against reds opening. 

Giving long, slow strokes, circling his clit before plunging in deep. "aaahHHh~!" Red practically screamed in pleasure as fell started to roughly pound into him, leaning forward to pin his boney wrists together. Fell leaned his skull in to kiss red deeply, swiping his tongue along his teeth and the inside of his mouth, fighting for dominance.

Soon their little tongue battle ended, fell of course coming out victorious. He breaks the kiss and starts trailing kisses down his brothers neck, suckling on his collar bone area to leave a hickey on the magic skin there. The action cause red to moan loudly as he desperately tried to fuck himself against that glorious length more. 

\- 

After hours and hours of dealing with their brothers monster induced heats, they finally got a break. Fell checked his phone to see 102 messages from undyne, groaning as he pushed himself up, fell got dressed and shuffled to the door. After a walk through the snow and a trip on the river boat he reached hotland, quickly making his way to the lab. He saw swap undyne hiding behind her alphys as fell undyne appeared to be yelling at her. 

With yet another groan he approached and listened as they talked about the culprit- culprits of what happened. In the corner where the computers were, were fell alphys watching the skeletons fun on repeat.


End file.
